Design Considerations for Variable Coupling Lumped Coil Systems

This paper investigates the impact of coupling variations and reflected impedance in an inductive power transfer (IPT) lumped coil system on the overall system behavior. It offers a process to quantify these variations and design the resonant networks to minimize these effects. An analytical analysis of the reactive power flow between the secondary and the primary power supply in this system is presented and validated by simulation and measurement. A 1.2-kW battery charging system consisting of an LCL primary network, circular pads, and a series tuned secondary is designed. It provides an example of how correct selection of the resonant networks provides minimal burden on the primary power supply due to the additional reactive power demands resulting from mistuning under variable coupling conditions.